1. Field of the Invention
This invention relates to a polymer dispersed liquid crystal optical device or liquid crystal film and in particular to a polymer dispersed liquid crystal optical device or liquid crystal film which is made functional by a light transmission and scattering mode and is used in display devices for displaying a character, picture, diagram, figure and etc. Light valves, light shutters, or the like, or switchable windows control transmission and cut-off of indecent light.
2. Description of the Related Art
Practical applications use conventional liquid crystal optical devices or liquid crystal films, TN type optical devices using nematic liquid crystal and STN type optical devices. In recent years, development on ferroelectric liquid crystal and antiferroelectric liquid crystal has been performed. However, these liquid crystals have heretofore required the use of a polarizer, thus there is a defect because these liquid crystals with a polarizer have restricted brightness and contrast.
In contrast thereto, WO 83/01016, the disclosure of which is hereby incorporated by reference herein. This disclosure teaches a method of encapsulating a liquid crystal material and dispersing such encapsulated liquid crystal material in a high molecular weight resin to give a polymer dispersed liquid crystal optical device. The optical device has a low attenuation of light because it does not require a polarizer. In this optical device, the encapsulated liquid crystal material alters a refractive index in the presence or absence of an electric field. Therefore, an encapsulating medium is selected so that it has a refractive index which is matched to that of the liquid crystal material under application of voltage. The resulting optical device becomes transparent when voltage is applied thereacross and becomes opaque due to light scattering when no voltage is applied thereacross. The polymer material for use in this prior art device includes polyvinyl alcohol, gelatin or the like.
Furthermore, optical devices which utilize a change in a refractive index of a liquid crystal material are known in which the liquid crystal material is dispersed in a two-pack system epoxy resin consisting of an uncured epoxy resin and a curing agent (WO 85/04262) and in an ultraviolet-curable resin (U.S. Pat. No. 4,728,547), the disclosures of which are hereby incorporated by reference herein.
In the above-mentioned polymer dispersed liquid crystal optical device in which the liquid crystal material is dispersed in the polymer material, a high driving voltage is required because of the strong interaction caused at an interface between the polymer material and the liquid crystal material.